Reflection type mask blank, and production method of the same

Abstract

To provide a reflection type mask blank capable of making a mask which prevents reduction of a reflectivity, improves a 3D effect, and has a high contrast.SOLUTION: A reflection type mask blank has a substrate 10, and a multilayered reflection film 50 formed on one main surface of the substrate 10 for reflecting exposure light. The multilayered reflection film 50 has a periodical laminate structure obtained by periodically laminating a low refractive index layer 30 containing ruthenium, a high refractive index layer 20 containing silicon, and a diffusion prevention layer 40 for preventing mutual diffusion of the ruthenium and the silicon. The diffusion prevention layer 40 is formed by contacting the low refractive index layer 30 with both or any one of a side proximal to the substrate 10 of the low refractive index layer 30 and a side separated from the substrate 10 of the low refractive index layer 30. The diffusion prevention layer 40 is constituted by one or more sublayers selected from a layer containing silicon nitride, a layer containing silicon carbide, a layer containing molybdenum, a layer containing molybdenum nitride, and a layer containing molybdenum carbide.SELECTED DRAWING: Figure 1A

Description

[Technical field]

[0001] The present invention relates to a reflective mask used in the manufacture of semiconductor devices such as LSIs, a reflective mask blank which is the material for the reflective mask, and a method for manufacturing a reflective mask. [Background technology]

[0002] In the manufacturing process of semiconductor devices (semiconductor device), photolithography technology is repeatedly used, in which exposure light is irradiated onto a transfer mask, and the circuit pattern formed on the mask is transferred onto a semiconductor substrate (semiconductor wafer) via a reduced projection optical system. Conventionally, the wavelength of the exposure light has mainly been 193 nm using argon fluoride (ArF) excimer laser light, and a process called multi-patterning, which combines exposure processes and processing processes multiple times, has been used to ultimately form patterns with dimensions smaller than the exposure wavelength.

[0003] However, as the device patterns continue to become finer, the formation of even finer patterns is now required, and so EUV lithography technology, which uses extreme ultraviolet (EUV) light with an even shorter wavelength than ArF excimer laser light as exposure light, has come to be used. EUV light is light with a wavelength of about 0.2 to 100 nm, more specifically, light with a wavelength of about 13.5 nm. EUV light has extremely low transparency to materials, and conventional transmission type projection optical systems and masks cannot be used, so reflective optical elements are used. For this reason, reflective masks have been proposed for pattern transfer.

[0004] A typical reflective mask has a multilayer reflective film that reflects EUV light formed on a substrate, and an absorber film that absorbs EUV light formed in a pattern on the multilayer reflective film. On the other hand, the state before the absorber film is patterned (including the state where a resist film is formed) is generally called a reflective mask blank, and this is used as the material for reflective masks.

[0005] A reflective mask blank has a basic structure including a low thermal expansion substrate and a multilayer reflective film formed thereon that reflects EUV light, and generally further includes an absorber film that absorbs EUV light formed on the multilayer reflective film. Summary of the Invention [Problem to be solved by the invention]

[0006] In EUV lithography, the exposure light is incident on the reflective mask at an oblique angle, and the mainstream practice is to set the incidence angle at 6 degrees with respect to the normal to the main surface of the reflective mask. Part of the exposure light incident at an oblique angle is blocked by the side walls of the absorber pattern, resulting in the so-called 3D effect (three-dimensional effect, shadowing effect). The 3D effect can cause positional and dimensional deviations in the transferred pattern, so a smaller 3D effect is preferable for miniaturizing patterns. The thinner the absorber pattern, the smaller the 3D effect, so a thinner film is desirable.

[0007] Meanwhile, in addition to the thickness of the absorber pattern, the structure of the multilayer reflective film also affects the 3D effect. Reflection of exposure light by the multilayer reflective film occurs due to the superposition of reflections occurring from the interfaces of each layer inside the multilayer reflective film, but a large contribution of reflections from positions deeper from the surface of the multilayer reflective film is a factor in increasing the 3D effect. Therefore, for multilayer reflective films, making the contribution of reflections from positions shallower from the surface relatively larger is advantageous in reducing the 3D effect.

[0008] Generally, multilayer reflective films have a periodic stacking structure in which low refractive index layers and high refractive index layers are alternately stacked, and multilayer reflective films in which molybdenum (Mo) and silicon (Si) are alternately stacked for approximately 40 cycles (Mo / Si multilayer reflective film) are known to efficiently reflect EUV light, and are currently used as the mainstream multilayer reflective film in EUV mask blanks.

[0009] Ruthenium (Ru) is a material with a lower refractive index and a higher absorption coefficient at a wavelength of 13.5 nm compared to molybdenum (Mo). Ruthenium (Ru) has a higher reflection coefficient at an ideal interface (an interface without mutual diffusion or roughness) with silicon (Si). Therefore, in a multilayer reflective film, when ruthenium (Ru) is used as a low refractive index layer, the contribution of reflection from the interface located shallower from the surface of the multilayer reflective film is greater, and the increase in reflectance with an increase in the number of layers in the multilayer reflective film is saturated at a smaller number of layers. On the other hand, since the absorption coefficient is larger, the loss due to the absorption effect increases as the number of layers in the multilayer reflective film increases. As a result, when the number of layers in the multilayer reflective film is small, the Ru / Si multilayer reflective film has a higher reflectance, but when the number of layers increases, the Mo / Si multilayer reflective film tends to have a higher reflectance.

[0010] When comparing layers with the same number, the Ru / Si multilayer reflective film has a relatively larger contribution of reflection from positions closer to the surface, and is therefore considered to be more advantageous in terms of the 3D effect.

[0011] However, in a Ru / Si multilayer reflective film, ruthenium (Ru) and silicon (Si) tend to form interdiffusion layers, which reduces the reflectance at each interface, making it difficult to obtain the expected reflectance. [Means for solving the problem]

[0012] The inventors of the present application have discovered that in a multilayer reflective film in which Ru and Si are alternately stacked, which contribute greatly to reflection from positions shallower than the surface of the multilayer reflective film, providing an anti-diffusion layer that effectively prevents interdiffusion of Ru and Si can prevent a decrease in reflectance, improve the 3D effect, and obtain a reflective mask blank that can create a high-contrast mask, thereby completing the present invention.

[0013] [Summary 1] The reflective mask blank according to the present invention comprises: A substrate; a multilayer reflective film formed on one main surface of the substrate and reflecting exposure light; Equipped with The multilayer reflective film has a periodic laminate structure in which a low refractive index layer containing ruthenium (Ru), a high refractive index layer containing silicon (Si), and a diffusion prevention layer that prevents interdiffusion of ruthenium (Ru) and silicon (Si) are periodically laminated, the diffusion prevention layer is formed in contact with the low refractive index layer on both or either one of a side of the low refractive index layer close to the substrate and a side of the low refractive index layer away from the substrate, The diffusion prevention layer may be composed of one or more sub-layers selected from a layer containing silicon nitride (SiN), a layer containing silicon carbide (SiC), a layer containing molybdenum (Mo), a layer containing molybdenum nitride (MoN) and a layer containing molybdenum carbide (MoC).

[0014] [Summary 2] In the reflective mask blank according to concept 1, The low refractive index layer may have a ruthenium content of 70 atomic % or more.

[0015] [Summary 3] In the reflective mask blank according to concept 1 or 2, the diffusion prevention layer includes a first diffusion prevention layer provided in contact with the low refractive index layer on a side thereof adjacent to the substrate, the first diffusion prevention layer has a first sublayer formed in contact with the high refractive index layer and a second sublayer formed in contact with the low refractive index layer, the first sublayer is a sublayer including at least one material selected from silicon nitride (SiN), silicon carbide (SiC), molybdenum nitride (MoN) and molybdenum carbide (MoC); the second sublayer is a sublayer containing molybdenum (Mo); The second sublayer may have a thickness of 0.2 nm to 0.8 nm.

[0016] [Summary 4] In the reflective mask blank according to concept 3, the diffusion prevention layer includes a second diffusion prevention layer in contact with the low refractive index layer on a side away from the substrate, The second diffusion prevention layer may have a layer containing molybdenum (Mo) formed in contact with the low refractive index layer, and the thickness of the layer may be 0.2 nm or more and 0.8 nm or less.

[0017] [Summary 5] The method for producing a reflective mask blank according to the present invention comprises the steps of: The multilayer reflective film of the reflective mask blank according to any one of Concepts 1 to 4 may be formed by a sputtering deposition method using a sputtering apparatus capable of mounting a plurality of targets in a chamber. Effect of the Invention

[0018] According to the present invention, a reflective mask blank is obtained that prevents a decrease in reflectance by providing an anti-diffusion layer that effectively prevents interdiffusion of Ru and Si in a multilayer reflective film having a structure in which Ru and Si are alternately stacked, which can increase the contribution of reflection from a position shallower from the surface of the multilayer reflective film, and reduces the 3D effect while enabling the production of a mask with high contrast during pattern transfer. [Brief description of the drawings]

[0019] [Figure 1A] FIG. 2 is a longitudinal sectional view showing an example in which a first anti-diffusion layer and a second anti-diffusion layer are provided in a reflective mask blank according to an embodiment of the present invention. [Figure 1B] FIG. 2 is a longitudinal sectional view showing an example in which a first anti-diffusion layer having a first sub-layer and a second sub-layer, and a second anti-diffusion layer are provided in a reflective mask blank according to an embodiment of the present invention. [Diagram 2] FIG. 2 is a longitudinal sectional view showing an example in which a first anti-diffusion layer is provided in a reflective mask blank according to an embodiment of the present invention. [Diagram 3] FIG. 4 is a longitudinal sectional view showing an example in which a second anti-diffusion layer is provided in the reflective mask blank according to the embodiment of the present invention. [Figure 4] FIG. 2 is a longitudinal sectional view showing an aspect in which an absorbing film pattern is formed in a reflective mask blank according to an embodiment of the present invention. [Diagram 5] FIG. 2 is a longitudinal sectional view showing an aspect in which an etching mask film is provided in a reflective mask blank according to an embodiment of the present invention. [Figure 6] FIG. 2 is a longitudinal sectional view showing an aspect in which an etching mask film and a resist film are provided in a reflective mask blank according to an embodiment of the present invention. [Figure 7] FIG. 2 is a longitudinal sectional view showing an aspect in which an etching mask film pattern is formed using a resist pattern as an etching mask in a reflective mask blank according to an embodiment of the present invention. [Figure 8] FIG. 1 is a vertical cross-sectional view illustrating a first embodiment of the present invention. [Figure 9] FIG. 13 is a vertical cross-sectional view for explaining Examples 9 to 12 of the present invention. [Figure 10] 1B is a longitudinal sectional view showing an embodiment in which a high refractive index layer is provided as the uppermost layer of the multilayer reflective film in the embodiment shown in FIG. 1A. FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0020] The embodiments of the present invention will be described in further detail below. The reflective mask blank of the present embodiment has a substrate 10 and a multilayer reflective film 50 formed on the substrate 10 (on one main surface (front surface) of the substrate 10) that reflects exposure light. The reflective mask blank of the present embodiment is suitable as a material (EUV mask blank) for a reflective mask (EUV mask) used in EUV lithography using EUV light as the exposure light. The wavelength of EUV light used in EUV lithography using EUV light as the exposure light is 13 to 14 nm, and typically has a wavelength of about 13.5 nm.

[0021] The substrate 10 preferably has low thermal expansion characteristics for use in EUV light exposure, and has a thermal expansion coefficient of, for example, ±2×10 -8 / ℃, preferably within ±5×10 -9 / °C. Examples of such materials include titania-doped quartz glass (SiO2-TiO2-based glass). It is preferable to use a substrate 10 with a sufficiently flat surface, and the surface roughness of the main surface of the substrate 10 is preferably 0.5 nm or less, more preferably 0.2 nm or less, in terms of RMS value. Such surface roughness can be obtained by polishing the substrate 10. The size of the main surface of the substrate 10 is preferably 152 mm square, and the thickness of the substrate 10 is 6.35 mm. The substrate 10 of this size is a so-called 6025 substrate (a substrate with a main surface size of 6 inches square and a thickness of 0.25 inches).

[0022] The multilayer reflective film 50 is a film that reflects EUV light, which is exposure light, in a reflective mask. The multilayer reflective film 50 may be provided in contact with one main surface of the substrate 10, or an undercoat film (not shown) may be provided between the substrate 10 and the multilayer reflective film 50. The multilayer reflective film 50 is a film that reflects EUV light, which is exposure light, in a reflective mask. The multilayer reflective film 50 has a periodic laminate structure in which high-refractive index layers 20 having a relatively high refractive index for EUV light and low-refractive index layers 30 having a relatively low refractive index for EUV light are alternately laminated. The number of cycles in the periodic laminate structure is preferably 10 cycles or more, particularly 20 cycles or more, and is preferably 50 cycles or less, particularly 40 cycles or less, and further preferably 30 cycles or less. The reflectance value is preferably 50% or more, particularly 55% or more, and further preferably 60% or more. Furthermore, the uppermost layer of the multilayer reflective film 50 may be a protective layer having a function of protecting the multilayer reflective film 50. In this case, a high refractive index layer (see the layer indicated by reference numeral 25 in FIG. 10) may be provided as the uppermost layer of the multilayer reflective film 50, and the high refractive index layer may have a function of protecting the multilayer reflective film 50. When a high refractive index layer is provided as the uppermost layer of the multilayer reflective film 50 in this manner, a protective film 110, an absorber film 120, etc., which will be described later, are provided on this high refractive index layer.

[0023] The multilayer reflective film 50 of the present embodiment has a layer containing silicon (Si) as the high refractive index layer 20, a layer containing ruthenium (Ru) as the low refractive index layer 30, and further has a diffusion prevention layer 40 that prevents interdiffusion of silicon (Si) and ruthenium (Ru).

[0024] The high refractive index layer 20 contains silicon (Si) and may contain at least one additive element selected from oxygen (O), nitrogen (N), carbon (C), boron (B) and hydrogen (H), or may be composed of a multilayer structure including a layer containing an additive element and a layer not containing an additive element. The thickness of the high refractive index layer 20 is preferably 2.5 nm or more and 5.5 nm or less, and more preferably 3 nm or more and 5 nm or less.

[0025] The low refractive index layer 30 is made of a material containing ruthenium (Ru), and may be ruthenium (Ru) alone or an alloy of ruthenium (Ru) and molybdenum (Mo). The ruthenium content of the low refractive index layer 30 is preferably 70 atomic % or more, and more preferably 80 atomic % or more. By increasing the ruthenium content of the low refractive index layer 30, the refractive index of the low refractive index layer 30 can be made lower, and the contribution of reflection from a position shallower from the surface of the multilayer reflective film 50 can be increased. The thickness of the low refractive index layer 30 is preferably 1 nm or more and 4 nm or less, and more preferably 1.5 nm or more and 3.5 nm or less.

[0026] The diffusion prevention layer 40 has an effect of preventing interdiffusion of ruthenium (Ru) and silicon (Si), and is composed of one or more sublayers selected from a layer containing silicon nitride (SiN), a layer containing silicon carbide (SiC), a layer containing molybdenum (Mo), a layer containing molybdenum nitride (MoN), and a layer containing molybdenum carbide (MoC). The diffusion prevention layer 40 may further contain hydrogen (H), boron (B), and oxygen (O). The thickness of the diffusion prevention layer 40 is preferably 0.2 nm or more and 1.3 nm or less.

[0027] The anti-diffusion layer 40 can be provided at either the interface of the low refractive index layer 30 on the side close to the substrate 10 or on the side away from the substrate 10, or at both interfaces, but is preferably provided at both interfaces. When the anti-diffusion layer 40 is provided at both interfaces of the low refractive index layer 30, the number, material, and thickness of the sublayers constituting the anti-diffusion layer 40 may be the same or different for both interfaces. Furthermore, the number, material, and thickness of the sublayers constituting each anti-diffusion layer 40 in one multilayer reflective film 50 may be the same or different for each layer.

[0028] For example, when the anti-diffusion layer 40 consists of only one sublayer, the anti-diffusion layer 40 may be formed in contact with at least one low refractive index layer 30 of the multilayer reflective film 50 on either the side close to the substrate 10 or the side away from the substrate 10, or on both sides. Alternatively, when providing an anti-diffusion layer 40 consisting of two sublayers, the anti-diffusion layer 40 consisting of a first sublayer 46 and a second sublayer 47 may be formed in contact with the low refractive index layer 30 on either or both of the side close to the substrate 10 and the side away from the substrate 10 of at least one low refractive index layer 30 of the multilayer reflective film 50. The diffusion prevention layer 40 is preferably provided on both the side of the low refractive index layer 30 close to the substrate 10 and the side remote from the substrate 10 .

[0029] In this embodiment, the diffusion prevention layer 40 provided on the side of the low refractive index layer 30 close to the substrate 10 is referred to as a first diffusion prevention layer 41. The first diffusion prevention layer 41 is preferably composed of a first sublayer 46 formed in contact with the high refractive index layer 20 and a second sublayer 47 formed in contact with the low refractive index layer 30 (see FIG. 1B). In this case, the first sublayer 46 is preferably a sublayer containing at least one material selected from silicon nitride (SiN), silicon carbide (SiC), molybdenum nitride (MoN) and molybdenum carbide (MoC), and the second sublayer 47 is preferably a sublayer containing molybdenum (Mo). It is effective to use molybdenum (Mo) as the material for the second sublayer 47, which is a material that is difficult to form an interdiffusion layer with ruthenium (Ru) in particular, has a low refractive index and a small absorption coefficient for EUV light. The first sublayer 46 has the effect of preventing diffusion of molybdenum (Mo) into the silicon (Si) layer when forming the diffusion prevention layer 40 containing molybdenum (Mo) after forming the high refractive index layer 20 containing silicon (Si). Effective materials for the first sublayer 46 include silicon nitride (SiN), silicon carbide (SiC), molybdenum nitride (MoN), and molybdenum carbide (MoC).

[0030] In such a configuration, the thickness of the second sublayer 47 is preferably 0.2 nm to 0.8 nm, inclusive, so that the contribution of reflection from a position shallower than the surface of the multilayer reflective film 50 can be kept large (the depth of the effective reflection surface becomes shallower).

[0031] In the present embodiment, the anti-diffusion layer 40 provided on the side of the low refractive index layer 30 that is away from the substrate 10 is referred to as a second anti-diffusion layer 42. This second anti-diffusion layer 42 is preferably a layer containing molybdenum (Mo), and from the viewpoints of the reflectance and effective reflection surface depth of the multilayer reflective film 50, it is preferable that the thickness of the second anti-diffusion layer 42 be 0.2 nm or more and 0.8 nm or less.

[0032] The method for forming the multilayer reflective film 50 includes a sputtering method in which power is supplied to a target, the atmospheric gas is turned into plasma (ionized) by the supplied power, and sputtering is performed, and an ion beam sputtering method in which an ion beam is irradiated onto the target. Examples of the sputtering method include a DC sputtering method in which a direct current voltage is applied to the target, and an RF sputtering method in which a high frequency voltage is applied to the target. The sputtering method is a film formation method in which a voltage is applied to the target with a sputtering gas introduced into a chamber, the gas is ionized, and the sputtering phenomenon caused by the gas ions is utilized, and the magnetron sputtering method in particular is advantageous in terms of productivity. The power applied to the target may be DC or RF, and DC also includes pulse sputtering in which a negative bias applied to the target is reversed for a short period of time to prevent the target from being charged up.

[0033] The multilayer reflective film 50 can be formed by a sputtering method using, for example, a sputtering device capable of mounting multiple targets. Specifically, the target can be appropriately selected from a ruthenium (Ru) target for forming a layer containing ruthenium (Ru), a silicon (Si) target for forming a layer containing silicon (Si), a molybdenum (Mo) target for forming a layer containing molybdenum (Mo), etc., and can be formed by using a rare gas such as neon (Ne) gas, argon (Ar) gas, krypton (Kr) gas, or xenon (Xe) gas as the sputtering gas.

[0034] When forming a layer containing molybdenum carbide (MoC) or a layer containing silicon carbide (SiC), it can be formed by applying a voltage to a carbon (C) target simultaneously with or separately from a molybdenum (Mo) target or a silicon (Si) target. Alternatively, it can be formed by using a molybdenum (Mo) target (molybdenum carbide (MoC) target) to which carbon (C) has been added, a silicon (Si) target (silicon carbide (SiC) target) to which carbon (C) has been added, or the like. Alternatively, it can be formed by reactive sputtering using a hydrocarbon gas such as methane (CH4) gas as a carbon source together with a rare gas.

[0035] When forming a layer containing molybdenum nitride (MoN) or a layer containing silicon nitride (SiN), it can be formed by reactive sputtering using a nitrogen-containing gas such as nitrogen gas together with a rare gas.

[0036] Furthermore, when forming a layer containing boron (B), a boron carbide (B4C) target, a molybdenum (Mo) target with boron (B) added (molybdenum boride (MoB) target), a silicon (Si) target with boron (B) added (silicon boride (SiB) target), etc. can be used.

[0037] The multilayer reflective film 50 may be provided with a protective film 110 for protecting the multilayer reflective film 50 (see FIGS. 1 to 7). A material containing ruthenium (Ru) is preferably used as the material for the protective film 110. The protective film 110 is required to protect the multilayer reflective film 50 from various dry etching and cleaning in the reflective mask manufacturing process, the exposure environment when the reflective mask is used, and cleaning treatment in the recycling process after use, and is preferably made of a material containing an additive element such as niobium (Nb), zirconium (Zr), titanium (Ti), rhodium (Rh) or the like to provide resistance to various processes, or may have a multilayer structure made of these materials.

[0038] The protective film 110 may be formed with another film between it and the multilayer reflective film 50, but is usually formed in contact with the multilayer reflective film 50.

[0039] The protective film 110 can be formed by, for example, a sputtering method. As a target, a ruthenium (Ru) target or a ruthenium (Ru) alloy target can be used to form a film or layer containing ruthenium (Ru), and a niobium (Nb) target or a niobium (Nb) alloy target can be used to form a film or layer containing niobium (Nb). Specifically, a ruthenium (Ru) target, a niobium (Nb) target, an alloy target of ruthenium (Ru) and niobium (Nb), etc. can be appropriately selected and used. The protective film 110 (each layer constituting the protective film 110) can be formed by sputtering using a rare gas such as neon (Ne) gas, argon (Ar) gas, krypton (Kr) gas, or xenon (Xe) gas as a sputtering gas, or by reactive sputtering using a reactive gas such as an oxygen-containing gas, a nitrogen-containing gas, or a carbon-containing gas together with the rare gas. Specific examples of reactive gases include oxygen (O2) gas, nitrogen (N2) gas, nitrous oxide (N2O) gas, nitric oxide (NO) gas, nitrogen dioxide (NO2) gas, and other nitrogen oxide gases, carbon monoxide (CO) gas, carbon dioxide (CO2) gas, and other carbon oxide gases. There are no particular limitations on the thickness of the protective film 110, but it is usually about 2 to 5 nm.

[0040] The reflective mask blank of this embodiment may further have an absorber film 120 that absorbs exposure light and functions as a pattern formation film on the protective film 110 (see FIGS. 1 to 7). In general, a reflective mask (EUV mask) is manufactured by forming a pattern on the absorber film 120 (see FIG. 4) using a reflective mask blank (EUV mask blank) that has a substrate 10, a multilayer reflective film 50, a protective film 110, and the absorber film 120.

[0041] Specific examples of such reflective mask blanks include those having a substrate 10, a multilayer reflective film 50 formed on one main surface of the substrate 10 and reflecting the exposure light, a protective film 110 formed on the multilayer reflective film 50, and an absorber film 120 formed on the protective film 110 and absorbing the exposure light. From the reflective mask blank having the multilayer reflective film 50, the protective film 110, and the absorber film 120, a reflective mask having the substrate 10, the multilayer reflective film 50 formed on one main surface of the substrate 10 and reflecting the exposure light, the protective film 110 formed on the multilayer reflective film 50, and a pattern (absorber pattern) of the absorber film 120 formed on the protective film 110 and absorbing the exposure light can be manufactured (see FIG. 4). The absorber film 120 is a film that absorbs the exposure light, specifically, EUV light, and reduces the reflectance.

[0042] The material of the absorber film 120 is not limited as long as it absorbs EUV light and can be patterned. Examples of the material of the absorber film 120 include materials containing tantalum (Ta) or chromium (Cr). Furthermore, materials containing Ta or Cr may contain oxygen (O), nitrogen (N), carbon (C), boron (B), and the like. Examples of materials containing Ta include Ta alone and tantalum compounds such as TaO, TaN, TaON, TaC, TaCN, TaCO, TaCON, TaB, TaOB, TaNB, TaONB, TaCB, TaCNB, TaCOB, and TaCONB. Examples of materials containing Cr include Cr alone and chromium compounds such as CrO, CrN, CrON, CrC, CrCN, CrCO, CrCON, CrB, CrOB, CrNB, CrONB, CrCB, CrCNB, CrCOB, and CrCONB.

[0043] The absorber film 120 can be formed by sputtering, and magnetron sputtering is preferable for sputtering. Specifically, it can be formed by sputtering using a metal target such as a chromium (Cr) target or a tantalum (Ta) target, or a metal compound target such as a chromium compound target or a tantalum compound target (a target containing a metal such as Cr or Ta and oxygen (O), nitrogen (N), carbon (C), boron (B), or the like) as a sputtering gas, and a rare gas such as neon (Ne) gas, argon (Ar) gas, krypton (Kr) gas, or xenon (Xe) gas, or by reactive sputtering using a rare gas and a reactive gas such as an oxygen-containing gas, a nitrogen-containing gas, or a carbon-containing gas. The thickness of the absorber film 120 is not particularly limited, but is usually about 40 to 80 nm.

[0044] A hard mask film 130 (an etching mask film for the absorber film 120) having etching characteristics different from those of the absorber film 120 may be provided on the side of the absorber film 120 away from the substrate 10, preferably in contact with the absorber film 120 (see FIG. 5). This hard mask film 130 functions as an etching mask when dry etching the absorber film 120. After the absorber pattern is formed, the hard mask film 130 may be left as a part of the absorber film 120 as a reflectance reducing layer for reducing the reflectance at the wavelength of light used in an inspection such as a pattern inspection, or may be removed so as not to remain on the reflective mask. Materials for the hard mask film 130 include materials containing chromium (Cr). The hard mask film 130 formed of a material containing Cr is particularly suitable when the absorber film 120 is formed of a material containing Ta but not containing Cr. When a layer (reflectance reducing layer) that mainly serves the function of reducing the reflectance at the wavelength of light used in inspection such as pattern inspection is formed on the absorber film 120, the hard mask film 130 can be formed on the reflectance reducing layer of the absorber film 120. The hard mask film 130 can be formed by, for example, a magnetron sputtering method. The film thickness of the hard mask film 130 is not particularly limited, but is usually about 5 to 20 nm.

[0045] The reflective mask blank may further have a conductive film 150 provided on the other main surface (back surface) of the substrate 10, which is the surface opposite to the one main surface, preferably in contact with the other main surface, for electrostatically chucking the reflective mask to an exposure tool (see Figures 1 to 7).

[0046] The conductive film 150 preferably has a sheet resistance of 100Ω / □ or less, and there is no particular limitation on the material. Examples of the material of the conductive film 150 include materials containing tantalum (Ta) or chromium (Cr). In addition, the materials containing tantalum (Ta) or chromium (Cr) may contain oxygen (O), nitrogen (N), carbon (C), boron (B), and the like. Examples of materials containing tantalum (Ta) include Ta alone, and tantalum (Ta) compounds such as TaO, TaN, TaON, TaC, TaCO, TaCN, TaCON, TaB, TaOB, TaNB, TaONB, TaCB, TaCOB, TaCNB, and TaCONB. Examples of materials containing chromium (Cr) include Cr alone, and chromium (Cr) compounds such as CrO, CrN, CrON, CrC, CrCO, CrCN, CrCON, CrB, CrOB, CrNB, CrONB, CrCB, CrCOB, CrCNB, and CrCONB.

[0047] The thickness of the conductive film 150 is not particularly limited as long as it functions as an electrostatic chuck, but is usually about 20 to 300 nm. The thickness of the conductive film 150 is preferably formed so that the film stress is balanced with the multilayer reflective film 50 and the pattern of the absorber film 120 (absorber pattern) after forming it as a reflective mask, particularly after forming the pattern of the absorber film 120 (absorber pattern). The conductive film 150 may be formed before forming the multilayer reflective film 50, or after forming all the films on the multilayer reflective film 50 side of the substrate 10, or may be formed after forming a part of the films on the multilayer reflective film 50 side of the substrate 10, and then the conductive film 150 may be formed, and then the remaining films on the multilayer reflective film 50 side of the substrate 10 may be formed. The conductive film 150 can be formed, for example, by magnetron sputtering.

[0048] The reflective mask blank may further include a resist film 140 formed on the side farthest from the substrate 10 (see FIG. 6). In this embodiment, the resist film 140 is preferably an electron beam (EB) resist. Also, the resist film 140 is preferably one that can be removed by SPM cleaning. Note that FIG. 7 shows the patterned resist film 140 and hard mask film 130.

[0049] The multilayer reflective film 50 shown in Figures 4 to 7 may adopt any of the embodiments shown in Figures 1A, 1B, 2, and 3. That is, the multilayer reflective film 50 shown in Figures 4 to 7 may be provided with a high refractive index layer 20, a first anti-diffusion layer 41, a low refractive index layer 30, and a second anti-diffusion layer 42 as repeating units as shown in Figures 1A and 1B, or may be provided with a high refractive index layer 20, a first anti-diffusion layer 41, and a low refractive index layer 30 as repeating units as shown in Figure 2, or may be provided with a high refractive index layer 20, a low refractive index layer 30, and a second anti-diffusion layer 42 as repeating units as shown in Figure 3. EXAMPLES

[0050] The present invention will be specifically described below with reference to examples and comparative examples, but the present invention is not limited to the following examples.

[0051] [Example 1] In Example 1, a sputtering device capable of mounting multiple targets on the substrate 10, a 152 mm square, 6.35 mm thick low thermal expansion glass substrate (SiO2-TiO2 glass substrate), and discharging the targets one by one or multiple targets simultaneously was used. The targets and the main surface of the substrate 10 were placed opposite each other, and the multilayer reflective film 50 was formed by DC magnetron sputtering while the substrate 10 was rotated. The embodiment of Example 1 is shown in FIG.

[0052] More specifically, a ruthenium (Ru) target and a silicon (Si) target were attached to a sputtering device, and a substrate 10 was placed thereon. First, power was applied to the silicon (Si) target while argon (Ar) gas (flow rate: 12 SCCM) was flowing into the chamber, a silicon (Si) layer having a thickness of 3.5 nm was formed as the high refractive index layer 20, and the application of power to the silicon (Si) target was stopped. Next, power was applied to the silicon (Si) target while argon gas (flow rate: 15 SCCM) and nitrogen (N2) gas (flow rate: 50 SCCM) were flowing into the chamber, and a silicon nitride (SiN) layer having a thickness of 0.5 nm was formed as the first diffusion prevention layer 41 on the side of the low refractive index layer 30 close to the substrate 10, and the application of power to the silicon (Si) target was stopped. Next, while argon gas (flow rate: 15 SCCM) was flowing in the chamber, power was applied to the ruthenium (Ru) target to form a ruthenium (Ru) layer having a thickness of 2.5 nm as the low refractive index layer 30, and the application of power to the ruthenium (Ru) target was stopped. Next, while argon gas (flow rate: 15 SCCM) and nitrogen (N2) gas (flow rate: 50 SCCM) were flowing in the chamber, power was applied to the silicon (Si) target to form a silicon nitride (SiN) layer having a thickness of 0.5 nm as the second diffusion prevention layer 42 on the side of the low refractive index layer 30 that is separated from the substrate 10, and the application of power to the silicon (Si) target was stopped. The operation of forming the high refractive index layer 20, the first diffusion prevention layer 41 on the side of the low refractive index layer 30 that is close to the substrate 10, the low refractive index layer 30, and the second diffusion prevention layer 42 on the side of the low refractive index layer 30 that is separated from the substrate 10 was one cycle, and this cycle was repeated to form a periodic stacked structure. The number of repetitions of the periodic laminate structure was 40 or 20. After forming the second anti-diffusion layer 42 on the side of the low refractive index layer 30 away from the substrate 10 in the last cycle, a 4 nm silicon (Si) layer (indicated as reference symbol 25 in FIG. 8) was finally formed as the uppermost layer of the multilayer reflective film 50 by the above-mentioned method, thereby forming the multilayer reflective film 50.

[0053] For the reflective mask blank consisting of the obtained substrate 10 and multilayer reflective film 50, the EUV reflectance at wavelengths of 13.1 to 14 nm was measured at an incident angle of 6 degrees, and the reflectance was maximum at 13.5 nm, and the value when the periodic stacking structure was repeated 40 cycles was 62.6%. In addition, the reflectance difference (R40-R20) between the reflectance when the periodic stacking structure was repeated 40 cycles and the reflectance when the periodic stacking structure was repeated 20 cycles was 3.3%.

[0054] [Example 2] A periodic laminate structure was formed in the same manner as in Example 1, except that a 4 nm thick silicon (Si) layer was formed as the high refractive index layer 20, and the second anti-diffusion layer 42 was not formed on the side of the low refractive index layer 30 that was remote from the substrate 10. The periodic laminate structure was repeated 40 cycles or 20 cycles. A 4.5 nm thick silicon (Si) layer was formed as the top layer of the multilayer reflective film 50 to form the multilayer reflective film 50, and a reflective mask blank consisting of the substrate 10 and the multilayer reflective film 50 was obtained.

[0055] The EUV reflectance of the obtained reflective mask blank was evaluated in the same manner as in Example 1. The reflectance was maximum at 13.5 nm, and the value was 62.1% when the periodic stacking structure was repeated 40 times. The reflectance difference (R40-R20) between the reflectance when the periodic stacking structure was repeated 40 times and the reflectance when the periodic stacking structure was repeated 20 times was 3.0%. Comparison with Example 1 shows that the reflectance (R40) is higher when the second diffusion prevention layer 42 is provided.

[0056] [Example 3] A ruthenium (Ru) target, a silicon (Si) target, and a molybdenum (Mo) target were mounted in a sputtering apparatus, and a silicon (Si) layer having a thickness of 4.5 nm was formed as the high refractive index layer 20; and as the first diffusion prevention layer 41 on the side of the low refractive index layer 30 adjacent to the substrate 10, power was applied to the molybdenum (Mo) target while flowing argon gas (flow rate: 30 SCCM) into the chamber, to form a molybdenum (Mo) layer having a thickness of 0.5 nm; and as the low refractive index layer 30, a ruthenium (Ru) layer having a thickness of 1.5 nm was formed; A reflective mask blank was obtained in the same manner as in Example 1, except that as the second diffusion prevention layer 42 on the side of the low refractive index layer 30 facing away from the substrate 10, power was applied to a molybdenum (Mo) target while argon gas (flow rate: 30 SCCM) was flowed into the chamber to form a molybdenum (Mo) layer having a thickness of 0.5 nm, and as the top layer of the multilayer reflective film 50, a silicon (Si) layer was formed to a thickness of 4.5 nm on the second diffusion prevention layer 42 on the side of the low refractive index layer 30 facing away from the substrate 10 in the last cycle.

[0057] For the obtained reflective mask blank, the EUV reflectance was measured in the same manner as in Example 1, and the reflectance reached a maximum at 13.5 nm, which was 60.2%.

[0058] [Example 4] A reflective mask blank was obtained in the same manner as in Example 3, except that as a first diffusion prevention layer 41 on the side of low refractive index layer 30 adjacent to substrate 10, power was applied to a molybdenum (Mo) target while argon gas (flow rate: 15 SCCM) and nitrogen gas (flow rate: 50 SCCM) were flowed into the chamber to form a molybdenum nitride (MoN) layer having a thickness of 0.5 nm, and as a second diffusion prevention layer 42 on the side of low refractive index layer 30 away from substrate 10, power was applied to a molybdenum (Mo) target while argon gas (flow rate: 15 SCCM) and nitrogen gas (flow rate: 50 SCCM) were flowed into the chamber to form a molybdenum nitride (MoN) layer having a thickness of 0.5 nm.

[0059] When the EUV reflectance of the obtained reflective mask blank was evaluated in the same manner as in Example 1, the reflectance reached a maximum at 13.5 nm, being 59.7%.

[0060] [Example 5] A reflective mask blank was obtained in the same manner as in Example 3, except that a molybdenum carbide (MoC) target was used instead of a molybdenum (Mo) target, and a molybdenum carbide (MoC) layer having a thickness of 0.5 nm was formed as a first diffusion prevention layer 41 on the side of low refractive index layer 30 adjacent to substrate 10 by applying power to the molybdenum carbide (MoC) target while flowing argon gas (flow rate: 30 SCCM) into the chamber, and a molybdenum carbide (MoC) layer having a thickness of 0.5 nm was formed as a second diffusion prevention layer 42 on the side of low refractive index layer 30 away from substrate 10 by applying power to the molybdenum carbide (MoC) target while flowing argon gas (flow rate: 30 SCCM) into the chamber.

[0061] When the EUV reflectance of the obtained reflective mask blank was evaluated in the same manner as in Example 1, the reflectance reached a maximum at 13.5 nm, being 61.2%.

[0062] [Examples 6 to 8] A periodic laminate structure was formed in the same manner as in Example 1, except that a ruthenium (Ru) target, a silicon (Si) target, and a molybdenum (Mo) target were mounted in a sputtering apparatus, and a ruthenium (Ru) target and a molybdenum (Mo) target were applied with electric power while argon gas (flow rate: 15 SCCM) was flowed into the chamber to form a ruthenium molybdenum (RuMo) alloy layer having a thickness of 2.5 nm as a low refractive index layer 30. The composition ratio (Ru:Mo) of ruthenium (Ru) and molybdenum (Mo) in the ruthenium molybdenum (RuMo) alloy layer was 3:1 in Example 6, 1:1 in Example 7, and 1:3 in Example 8. The number of repetitions of the periodic laminate structure was 40 cycles or 20 cycles. A silicon (Si) layer of 4 nm was formed as the top layer of the multilayer reflective film 50 by the above-mentioned method to form the multilayer reflective film 50, and a reflective mask blank consisting of the substrate 10 and the multilayer reflective film 50 was obtained.

[0063] The EUV reflectance of the obtained reflective mask blank was evaluated in the same manner as in Example 1. The reflectance was maximum at 13.5 nm, and the value at 40 cycles of repetition of the periodic stack structure was 64.0% in Example 6, 62.1% in Example 7, and 61.2% in Example 8. The difference (R40-R20) between the reflectance at 40 cycles of repetition of the periodic stack structure and the reflectance at 20 cycles was 4.7% in Example 6, 5.7% in Example 7, and 7.4% in Example 8. From the comparison of Example 1 and Examples 6 to 8, it can be seen that the higher the ruthenium (Ru) content of the low refractive index layer 30, the smaller the difference between the reflectance at 40 cycles and the reflectance at 20 cycles, and therefore the contribution of reflection from a position shallower than the surface of the multilayer reflective film 50 becomes relatively large. In particular, it is shown that the reflectance at 20 cycles becomes high for Examples 1 and 6, in which the ruthenium (Ru) content is 70 atomic % or more.

[0064] [Examples 9 to 12] A ruthenium (Ru) target, a silicon (Si) target, and a molybdenum (Mo) target were attached to the sputtering device, and the substrate 10 was placed thereon. First, while argon (Ar) gas (flow rate: 12 SCCM) was flowing into the chamber, power was applied to the silicon (Si) target to form a 4 nm thick silicon (Si) layer as the high refractive index layer 20, and the application of power to the silicon (Si) target was stopped. Next, while argon gas (flow rate: 15 SCCM) and nitrogen (N2) gas (flow rate: 50 SCCM) were flowing into the chamber, power was applied to the silicon (Si) target to form a 0.5 nm thick silicon nitride (SiN) layer as the first sublayer 46 of the first diffusion prevention layer 41 on the side of the low refractive index layer 30 close to the substrate 10, and the application of power to the silicon (Si) target was stopped. Next, while argon gas (flow rate: 30 SCCM) was flowing in the chamber, power was applied to the molybdenum (Mo) target to form a molybdenum (Mo) layer as the second sublayer 47 of the first diffusion prevention layer 41 on the side of the low refractive index layer 30 close to the substrate 10, and the application of power to the molybdenum (Mo) target was stopped. Next, while argon gas (flow rate: 15 SCCM) was flowing in the chamber, power was applied to the ruthenium (Ru) target to form a ruthenium (Ru) layer as the low refractive index layer 30, and the application of power to the ruthenium (Ru) target was stopped. Next, while argon gas (flow rate: 30 SCCM) was flowing in the chamber, power was applied to the molybdenum (Mo) target to form a molybdenum (Mo) layer as the second diffusion prevention layer 42 on the side of the low refractive index layer 30 away from the substrate 10, and the application of power to the molybdenum (Mo) target was stopped. The aspects of Examples 9 to 12 are shown in FIG. 9.

[0065] The thickness of the second sublayer 47 (molybdenum (Mo) layer) of the first diffusion prevention layer 41 on the side of the low refractive index layer 30 closest to the substrate 10 was 0.2 nm in Example 9, 0.5 nm in Example 10, 0.8 nm in Example 11, and 1 nm in Example 12.

[0066] The thickness of the low refractive index layer 30 (ruthenium (Ru) layer) was 2.1 nm in Example 9, 1.5 nm in Example 10, 0.9 nm in Example 11, and 0.5 nm in Example 12. The thickness of the second diffusion prevention layer 42 (molybdenum (Mo) layer) on the side of the low refractive index layer 30 away from the substrate 10 was 0.2 nm in Example 9, 0.5 nm in Example 10, 0.8 nm in Example 11, and 1 nm in Example 12.

[0067] The operation of forming the high refractive index layer 20, the first sublayer 46 of the first anti-diffusion layer 41 on the side of the low refractive index layer 30 close to the substrate 10, the second sublayer 47 of the first anti-diffusion layer 41 on the side of the low refractive index layer 30 close to the substrate 10, the low refractive index layer 30, and the second anti-diffusion layer 42 on the side of the low refractive index layer 30 away from the substrate 10 was defined as one cycle, and this cycle was repeated to form a periodic laminate structure. The number of repetitions of the periodic laminate structure was 40 or 20 cycles. After forming the second anti-diffusion layer 42 on the side of the low refractive index layer 30 away from the substrate 10 in the last cycle, finally, a silicon (Si) layer of 4.5 nm (shown as reference numeral 25 in FIG. 9) was formed as the top layer of the multilayer reflective film 50 by the above-mentioned method to form the multilayer reflective film 50, and a reflective mask blank consisting of the substrate 10 and the multilayer reflective film 50 was obtained.

[0068] The EUV reflectance of the obtained reflective mask blank was evaluated in the same manner as in Example 1. The reflectance was maximum at 13.5 nm, and the value at 40 repetitions of the periodic stacked structure was 65.1% in Example 9, 66.5% in Example 10, 66.9% in Example 11, and 66.0% in Example 12. In addition, the difference in reflectance (R40) at 40 repetitions of the periodic stacked structure and the reflectance (R20) at 20 repetitions (R40-R20) was 3.7% in Example 9, 4.9% in Example 10, 6.0% in Example 11, and 8.2% in Example 12.

[0069] A comparison of Examples 2 and 9 to 12 reveals that the thicker the molybdenum layer of the anti-diffusion layer 40 is, the greater the difference between the reflectance at 40 cycles and the reflectance at 20 cycles is, and therefore the contribution of reflection from a shallow position from the surface of the multilayer reflective film 50 becomes relatively smaller.

[0070] Furthermore, by setting the thickness of the second sublayer 47 (molybdenum (Mo) layer) of the first diffusion prevention layer 41 on the side of the low refractive index layer 30 closest to the substrate 10 and the thickness of the second diffusion prevention layer 42 (molybdenum (Mo) layer) on the side of the low refractive index layer 30 away from the substrate 10 to be 0.2 nm or more and 0.8 nm or less, the reflectance of both the 20-cycle periodic structure and the 40-cycle periodic structure becomes particularly high, indicating that the contribution of reflection from a position shallower from the surface of the multilayer reflective film 50 can be increased and that the effect of preventing diffusion between layers is high.

[0071] [Comparative Example 1] A periodic laminate structure was formed in the same manner as in Example 1, except that a 4.5 nm thick silicon (Si) layer was formed as the high refractive index layer 20, the first anti-diffusion layer 41 was not formed on the side of the low refractive index layer 30 close to the substrate 10, and the second anti-diffusion layer 42 was not formed on the side of the low refractive index layer 30 away from the substrate 10. The periodic laminate structure was repeated 40 times. A 4.5 nm thick silicon (Si) layer was formed as the top layer of the multilayer reflective film 50 to form the multilayer reflective film 50, and a reflective mask blank consisting of the substrate 10 and the multilayer reflective film 50 was obtained.

[0072] The EUV reflectance of the obtained reflective mask blank was evaluated in the same manner as in Example 1, and the reflectance was maximum at 13.5 nm, and the value was 58.7% in Comparative Example 1. Thus, the reflectance was low when the diffusion prevention layer 40 was not provided. Comparing Examples 1, 3, 4, and 5 with Comparative Example 1, it is recognized that the silicon nitride (SiN) layer, molybdenum (Mo) layer, molybdenum nitride (MoN) layer, and molybdenum carbide (MoC) layer have improved reflectance due to their diffusion prevention effects.

[0073] [Comparative Example 2] A periodic laminate structure was formed in the same manner as in Example 2, except that a molybdenum (Mo) target and a silicon (Si) target were mounted in a sputtering apparatus, and a molybdenum (Mo) layer having a thickness of 2.5 nm was formed as the low refractive index layer 30 by applying power to the molybdenum (Mo) target while flowing argon gas (flow rate: 15 SCCM) in the chamber. A silicon (Si) layer having a thickness of 4.5 nm was formed as the uppermost layer of the multilayer reflective film 50 to form the multilayer reflective film 50, and a reflective mask blank consisting of the substrate 10 and the multilayer reflective film 50 was obtained.

[0074] For the obtained reflective mask blank, the difference in reflectance (R40-R20) between the reflectance when the periodic stack structure was repeated 40 cycles (R40) and the reflectance when the periodic stack structure was repeated 20 cycles was evaluated in the same manner as in Example 1, and was found to be 11.7%.

[0075] The relatively large difference in reflectance between 40 and 20 cycles in the periodic stack structure of Comparative Example 2 means that the contribution of reflection from a shallow position from the surface of the multilayer reflective film 50 is relatively small. In contrast, the periodic stack structure of Example 2 shows a relatively small difference between the reflectance between 40 and 20 cycles, indicating that the contribution of reflection from a shallow position from the surface of the multilayer reflective film 50 is relatively large. [Explanation of symbols]

[0076] 10 Substrate 20 High refractive index layer 30 Low refractive index layer 40 Diffusion prevention layer 41 First diffusion prevention layer 42 Second diffusion prevention layer 46 First Sublayer 47 Second Sublayer 50 Multilayer reflective coating

Claims

1. A substrate; a multilayer reflective film formed on one main surface of the substrate and reflecting exposure light; Equipped with The multilayer reflective film has a periodic laminate structure in which a low refractive index layer containing ruthenium (Ru), a high refractive index layer containing silicon (Si), and a diffusion prevention layer that prevents interdiffusion of ruthenium (Ru) and silicon (Si) are periodically laminated, the diffusion prevention layer is formed in contact with the low refractive index layer on both or either one of a side of the low refractive index layer close to the substrate and a side of the low refractive index layer away from the substrate, a diffusion prevention layer comprising one or more sub-layers selected from a layer containing silicon nitride (SiN), a layer containing silicon carbide (SiC), a layer containing molybdenum (Mo), a layer containing molybdenum nitride (MoN), and a layer containing molybdenum carbide (MoC).

2. 2. The reflective mask blank according to claim 1, wherein the low refractive index layer has a ruthenium content of 70 atomic % or more.

3. the diffusion prevention layer includes a first diffusion prevention layer provided in contact with the low refractive index layer on a side thereof adjacent to the substrate, the first diffusion prevention layer has a first sublayer formed in contact with the high refractive index layer and a second sublayer formed in contact with the low refractive index layer, the first sublayer is a sublayer including at least one material selected from silicon nitride (SiN), silicon carbide (SiC), molybdenum nitride (MoN), and molybdenum carbide (MoC); the second sublayer is a sublayer containing molybdenum (Mo); 2. The reflective mask blank according to claim 1, wherein the second sublayer has a thickness of 0.2 nm to 0.8 nm.

4. the diffusion prevention layer includes a second diffusion prevention layer provided in contact with the low refractive index layer on a side away from the substrate, 4. The reflective mask blank according to claim 3, wherein the second diffusion prevention layer has a layer containing molybdenum (Mo) formed in contact with the low refractive index layer and has a thickness of 0.2 nm or more and 0.8 nm or less.

5. A method for producing a reflective mask blank, comprising forming the multilayer reflective film of the reflective mask blank according to any one of claims 1 to 4 by a sputtering deposition method using a sputtering apparatus capable of mounting a plurality of targets in a chamber.

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